Methods of manufacturing therapeutic proteins

ABSTRACT

Disclosed herein are methods of manufacturing therapeutic proteins.

CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No. 15/570,178, filed on Oct. 27, 2017, which is a U.S. National Stage Entry of PCT/US2016/029472, filed Apr. 27, 2016, which claims benefit of U.S. Provisional Patent Application No. 62/153,178 filed on Apr. 27, 2015.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Jul. 1, 2020, is named 53744_701_301_SEQUENCE LISTING and is 26,682 bytes in size.

BACKGROUND OF THE INVENTION

The production of therapeutic proteins using mammalian cell expression systems is of growing importance within the biotechnology industry. Various culture and transfection systems have been described, but each has significant limitations.

SUMMARY OF THE INVENTION

The invention described herein is based, in part, on the discovery that the combination of cholesterol-auxotrophic cells with one or more additional selection markers can be exploited in methods of manufacturing therapeutic proteins, to avoid unexpected manufacturing complications associated with cholesterol-auxotrophic cells (e.g., low productivity). In one aspect, the disclosure features methods of manufacturing a therapeutic protein, the method comprising: culturing a cholesterol-auxotrophic and glutamine-auxotrophic cell; transfecting the cell with (i) a nucleic acid encoding a protein which is capable of restoring cholesterol biosynthesis in the cell; (ii) a nucleic acid encoding a protein which is capable of restoring glutamine biosynthesis in the cell; and (iii) a nucleic acid encoding the therapeutic protein; culturing the cell under conditions suitable for expression of the therapeutic protein; and isolating and/or purifying the therapeutic protein.

In one embodiment, the cell is an NS0 cell.

In some embodiments, the therapeutic protein is an antibody. In some embodiments, the therapeutic protein is a fusion protein. In some embodiments, the therapeutic protein is an Fc-containing fusion protein.

In some embodiments, in the transfecting step the cell is transfected with nucleic acids (iii) encoding an antibody light chain and an antibody heavy chain. In some embodiments, nucleic acid (i) encodes a 3-ketosteroid reductase. In some embodiments, the nucleic acid (ii) encodes a glutamine synthetase.

In some embodiments, a first expression vector comprises nucleic acid (i) and (iii), and a second expression vector comprises nucleic acids (ii). In some embodiments, a first expression vector comprises nucleic acid (i), and a second expression vector comprises nucleic acids (ii) and (iii). In some embodiments, transfection of the first expression vector is performed prior to transfection of the second expression vector. In some embodiments, transfection of the first expression vector is performed simultaneously with transfection of the second expression vector.

In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (i)) in the absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (ii)) in the absence of exogenously introduced glutamine. In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (ii)) in the presence of a glutamine synthetase inhibitor (e.g., methionine sulfoximine). In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (i)) in the presence of a 3-ketosteriod reductase inhibitor.

In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol and in the absence of exogenously introduced glutamine. In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol, in the absence of exogenously introduced glutamine, and in the presence of a glutamine synthetase inhibitor (e.g., methionine sulfoximine). In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (i)) in the absence of exogenously introduced cholesterol and the cell is cultured (e.g., after transfection of nucleic acid (ii)) in the absence of exogenously introduced glutamine.

In one aspect, the disclosure features methods of manufacturing a therapeutic protein, the method comprising: culturing a cholesterol-auxotrophic cell; transfecting the cell with (i) a nucleic acid encoding a protein which is capable of restoring cholesterol biosynthesis in the cell; (ii) a nucleic acid encoding a protein expressing one or more selectable marker; and (iii) a nucleic acid encoding the therapeutic protein; culturing the cell under conditions suitable for expression of the therapeutic protein; and isolating and/or purifying the therapeutic protein.

In one embodiment, the cell is an NS0 cell.

In some embodiments, the therapeutic protein is an antibody. In some embodiments, the therapeutic protein is a fusion protein. In some embodiments, the therapeutic protein is an Fc-containing fusion protein.

In some embodiments, in the transfecting step the cell is transfected with nucleic acids (iii) encoding an antibody light chain and an antibody heavy chain.

In some embodiments, nucleic acid (i) encodes a 3-ketosteroid reductase.

In some embodiments, the nucleic acid (ii) encodes a glutamine synthetase, a dihydrofolate reductase (DHFR), or one or more antibiotic resistance gene (e.g., neomycin, blasticidin, hygromyocin, puromycin, zeocin, mycophenolic acid).

In some embodiments, a first expression vector comprises nucleic acid (i) and (iii), and a second expression vector comprises nucleic acids (ii). In some embodiments, a first expression vector comprises nucleic acid (i), and a second expression vector comprises nucleic acids (ii) and (iii). In some embodiments, transfection of the first expression vector is performed prior to transfection of the second expression vector. In some embodiments, transfection of the first expression vector is performed simultaneously with transfection of the second expression vector.

In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (i)) in the absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (i)) in the presence of a 3-ketosteriod reductase inhibitor. In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol.

In one aspect, the disclosure features methods of manufacturing a therapeutic protein, the method comprising: culturing a cholesterol-auxotrophic cell that does not express a functional dihydrofolate reductase (DHFR); transfecting the cell with (i) a nucleic acid encoding a protein which is capable of restoring cholesterol biosynthesis in the cell; (ii) a nucleic acid encoding a DHFR; and (iii) a nucleic acid encoding the therapeutic protein; culturing the cell under conditions suitable for expression of the therapeutic protein; and isolating and/or purifying the therapeutic protein.

In one embodiment, the cell is an NS0 cell.

In some embodiments, the therapeutic protein is an antibody. In some embodiments, the therapeutic protein is a fusion protein. In some embodiments, the therapeutic protein is an Fc-containing fusion protein.

In some embodiments, in the transfecting step the cell is transfected with nucleic acids (iii) encoding an antibody light chain and an antibody heavy chain. In some embodiments, nucleic acid (i) encodes a 3-ketosteroid reductase.

In some embodiments, a first expression vector comprises nucleic acid (i) and (iii), and a second expression vector comprises nucleic acids (ii). In some embodiments, a first expression vector comprises nucleic acid (i), and a second expression vector comprises nucleic acids (ii) and (iii). In some embodiments, transfection of the first expression vector is performed prior to transfection of the second expression vector. In some embodiments, transfection of the first expression vector is performed simultaneously with transfection of the second expression vector.

In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (i)) in the absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (ii)) in the presence of a DHFR inhibitor (e.g., methionine sulphoximine (MSX)). In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (i)) in the presence of a 3-ketosteriod reductase inhibitor.

In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol and in the presence of a DHFR inhibitor (e.g., methionine sulphoximine (MSX)).

In one aspect, the disclosure features methods of manufacturing a therapeutic protein, the method comprising: culturing a cholesterol-auxotrophic cell that is sensitive to neomycin; transfecting the cell with (i) a nucleic acid encoding a protein which is capable of restoring cholesterol biosynthesis in the cell; (ii) a nucleic acid encoding a neomycin resistance gene; and (iii) a nucleic acid encoding the therapeutic protein; culturing the cell under conditions suitable for expression of the therapeutic protein; and isolating and/or purifying the therapeutic protein.

In one embodiment, the cell is an NS0 cell.

In some embodiments, the therapeutic protein is an antibody. In some embodiments, the therapeutic protein is a fusion protein. In some embodiments, the therapeutic protein is an Fc-containing fusion protein.

In some embodiments, in the transfecting step the cell is transfected with nucleic acids (iii) encoding an antibody light chain and an antibody heavy chain. In some embodiments, nucleic acid (i) encodes a 3-ketosteroid reductase. In some embodiments, the nucleic acid (ii) encodes the neomycin resistance gene from Tn5 encoding an aminoglycoside 3′-phosphotransferase (APH 3′ II).

In some embodiments, a first expression vector comprises nucleic acid (i) and (iii), and a second expression vector comprises nucleic acids (ii). In some embodiments, a first expression vector comprises nucleic acid (i), and a second expression vector comprises nucleic acids (ii) and (iii). In some embodiments, transfection of the first expression vector is performed prior to transfection of the second expression vector. In some embodiments, transfection of the first expression vector is performed simultaneously with transfection of the second expression vector.

In some embodiments, both the first and second expression vector contains HC and LC one vector contains KSR and the other vector contains GS or another antibiotic resistant gene. In some embodiments, there are three separate vectors (e.g., for triple selection), wherein all three vectors contains HC and LC; a first vector contains KSR, a second vector contains GS, and a third vector contains any antibiotic resistant gene, e.g. NEO.

In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (i)) in the absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (ii)) in the presence of an aminoglycoside antibiotic (e.g., G418). In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (i)) in the presence of a 3-ketosteriod reductase inhibitor.

In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol and in the presence of an aminoglycoside antibiotic (e.g., G418).

In one aspect, the disclosure features methods of manufacturing a therapeutic protein, the method comprising: culturing a cholesterol-auxotrophic cell that is sensitive to blasticidin; transfecting the cell with (i) a nucleic acid encoding a protein which is capable of restoring cholesterol biosynthesis in the cell; (ii) a nucleic acid encoding a blasticidin resistance gene; and (iii) a nucleic acid encoding the therapeutic protein; culturing the cell under conditions suitable for expression of the therapeutic protein; and isolating and/or purifying the therapeutic protein.

In one embodiment, the cell is an NS0 cell.

In some embodiments, the therapeutic protein is an antibody. In some embodiments, the therapeutic protein is a fusion protein. In some embodiments, the therapeutic protein is an Fc-containing fusion protein.

In some embodiments, in the transfecting step the cell is transfected with nucleic acids (iii) encoding an antibody light chain and an antibody heavy chain. In some embodiments, nucleic acid (i) encodes a 3-ketosteroid reductase. In some embodiments, the nucleic acid (ii) encodes the blasticidin resistance gene from Bacillus cereus (which codes for blasticidin-S deaminase).

In some embodiments, a first expression vector comprises nucleic acid (i) and (iii), and a second expression vector comprises nucleic acids (ii). In some embodiments, a first expression vector comprises nucleic acid (i), and a second expression vector comprises nucleic acids (ii) and (iii). In some embodiments, transfection of the first expression vector is performed prior to transfection of the second expression vector. In some embodiments, transfection of the first expression vector is performed simultaneously with transfection of the second expression vector.

In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (i)) in the absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (ii)) in the presence of a peptidyl nucleoside antibiotic (e.g., blasticidin). In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (i)) in the presence of a 3-ketosteriod reductase inhibitor.

In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol and in the presence of a peptidyl nucleoside antibiotic an aminoglycoside antibiotic (e.g., blasticidin).

In one aspect, the disclosure features methods of manufacturing a therapeutic protein, the method comprising: culturing a cholesterol-auxotrophic cell that is sensitive to hygromycin B; transfecting the cell with (i) a nucleic acid encoding a protein which is capable of restoring cholesterol biosynthesis in the cell; (ii) a nucleic acid encoding a hygromycin B resistance gene; and (iii) a nucleic acid encoding the therapeutic protein; culturing the cell under conditions suitable for expression of the therapeutic protein; and isolating and/or purifying the therapeutic protein.

In one embodiment, the cell is an NS0 cell.

In some embodiments, the therapeutic protein is an antibody. In some embodiments, the therapeutic protein is a fusion protein. In some embodiments, the therapeutic protein is an Fc-containing fusion protein.

In some embodiments, in the transfecting step the cell is transfected with nucleic acids (iii) encoding an antibody light chain and an antibody heavy chain. In some embodiments, nucleic acid (i) encodes a 3-ketosteroid reductase. In some embodiments, the nucleic acid (ii) encodes a hygromycin B phosphotransferase.

In some embodiments, a first expression vector comprises nucleic acid (i) and (iii), and a second expression vector comprises nucleic acids (ii). In some embodiments, a first expression vector comprises nucleic acid (i), and a second expression vector comprises nucleic acids (ii) and (iii). In some embodiments, transfection of the first expression vector is performed prior to transfection of the second expression vector. In some embodiments, transfection of the first expression vector is performed simultaneously with transfection of the second expression vector.

In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (i)) in the absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (ii)) in the presence of an aminoglycoside antibiotic (e.g., hygromycin B). In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (i)) in the presence of a 3-ketosteriod reductase inhibitor.

In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol and in the presence of a peptidyl nucleoside antibiotic an aminoglycoside antibiotic (e.g., hygromycin B).

In one aspect, the disclosure features methods of manufacturing a therapeutic protein, the method comprising: culturing a cholesterol-auxotrophic cell that is sensitive to puromycin; transfecting the cell with (i) a nucleic acid encoding a protein which is capable of restoring cholesterol biosynthesis in the cell; (ii) a nucleic acid encoding a puromycin resistance gene; and (iii) a nucleic acid encoding the therapeutic protein; culturing the cell under conditions suitable for expression of the therapeutic protein; and isolating and/or purifying the therapeutic protein.

In one embodiment, the cell is an NS0 cell.

In some embodiments, the therapeutic protein is an antibody. In some embodiments, the therapeutic protein is a fusion protein. In some embodiments, the therapeutic protein is an Fc-containing fusion protein.

In some embodiments, in the transfecting step the cell is transfected with nucleic acids (iii) encoding an antibody light chain and an antibody heavy chain. In some embodiments, nucleic acid (i) encodes a 3-ketosteroid reductase. In some embodiments, the nucleic acid (ii) encodes a puromycin N-acetyl-transferase.

In some embodiments, a first expression vector comprises nucleic acid (i) and (iii), and a second expression vector comprises nucleic acids (ii). In some embodiments, a first expression vector comprises nucleic acid (i), and a second expression vector comprises nucleic acids (ii) and (iii). In some embodiments, transfection of the first expression vector is performed prior to transfection of the second expression vector. In some embodiments, transfection of the first expression vector is performed simultaneously with transfection of the second expression vector.

In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (i)) in the absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (ii)) in the presence of an aminonucleoside antibiotic (e.g., puromycin). In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (i)) in the presence of a 3-ketosteriod reductase inhibitor.

In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol and in the presence of a peptidyl nucleoside antibiotic an aminonucleoside antibiotic (e.g., puromycin).

In one aspect, the disclosure features methods of manufacturing a therapeutic protein, the method comprising: culturing a cholesterol-auxotrophic cell that is sensitive to zeocin; transfecting the cell with (i) a nucleic acid encoding a protein which is capable of restoring cholesterol biosynthesis in the cell; (ii) a nucleic acid encoding a zeocin resistance gene; and (iii) a nucleic acid encoding the therapeutic protein; culturing the cell under conditions suitable for expression of the therapeutic protein; and isolating and/or purifying the therapeutic protein.

In one embodiment, the cell is an NS0 cell.

In some embodiments, the therapeutic protein is an antibody. In some embodiments, the therapeutic protein is a fusion protein. In some embodiments, the therapeutic protein is an Fc-containing fusion protein.

In some embodiments, in the transfecting step the cell is transfected with nucleic acids (iii) encoding an antibody light chain and an antibody heavy chain. In some embodiments, nucleic acid (i) encodes a 3-ketosteroid reductase. In some embodiments, the nucleic acid (ii) encodes a Sh ble gene product.

In some embodiments, a first expression vector comprises nucleic acid (i) and (iii), and a second expression vector comprises nucleic acids (ii). In some embodiments, a first expression vector comprises nucleic acid (i), and a second expression vector comprises nucleic acids (ii) and (iii). In some embodiments, transfection of the first expression vector is performed prior to transfection of the second expression vector. In some embodiments, transfection of the first expression vector is performed simultaneously with transfection of the second expression vector.

In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (i)) in the absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (ii)) in the presence of a copper-chelated glycopeptide antibiotic (e.g., zeocin). In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (i)) in the presence of a 3-ketosteriod reductase inhibitor. In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol and in the presence of a copper-chelated glycopeptide antibiotic (e.g., zeocin).

In one aspect, the disclosure features methods of manufacturing a therapeutic protein, the method comprising: culturing a cholesterol-auxotrophic cell that is sensitive to mycophenolic Acid (MPA); transfecting the cell with (i) a nucleic acid encoding a protein which is capable of restoring cholesterol biosynthesis in the cell; (ii) a nucleic acid encoding a MPA resistance gene; and (iii) a nucleic acid encoding the therapeutic protein; culturing the cell under conditions suitable for expression of the therapeutic protein; and isolating and/or purifying the therapeutic protein.

In one embodiment, the cell is an NS0 cell.

In some embodiments, the therapeutic protein is an antibody. In some embodiments, the therapeutic protein is a fusion protein. In some embodiments, the therapeutic protein is an Fc-containing fusion protein.

In some embodiments, in the transfecting step the cell is transfected with nucleic acids (iii) encoding an antibody light chain and an antibody heavy chain. In some embodiments, nucleic acid (i) encodes a 3-ketosteroid reductase. In some embodiments, the nucleic acid (ii) encodes the xanthine-guanine phosphoribosyltransferase (Ecogpt) gene.

In some embodiments, a first expression vector comprises nucleic acid (i) and (iii), and a second expression vector comprises nucleic acids (ii). In some embodiments, a first expression vector comprises nucleic acid (i), and a second expression vector comprises nucleic acids (ii) and (iii). In some embodiments, transfection of the first expression vector is performed prior to transfection of the second expression vector. In some embodiments, transfection of the first expression vector is performed simultaneously with transfection of the second expression vector.

In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (i)) in the absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (ii)) in the presence of MPA. In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (i)) in the presence of a 3-ketosteriod reductase inhibitor.

In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol and in the presence of MPA.

In one aspect, the disclosure features methods of manufacturing a therapeutic protein, the method comprising: culturing a cholesterol-auxotrophic cell that is sensitive to mycophenolic acid (MPA); transfecting the cell with (i) a nucleic acid encoding a protein which is capable of restoring cholesterol biosynthesis in the cell; (ii) a nucleic acid encoding a MPA resistance gene; and (iii) a nucleic acid encoding the therapeutic protein; culturing the cell under conditions suitable for expression of the therapeutic protein; and isolating and/or purifying the therapeutic protein.

In one embodiment, the cell is an NS0 cell.

In some embodiments, the therapeutic protein is an antibody. In some embodiments, the therapeutic protein is a fusion protein. In some embodiments, the therapeutic protein is an Fc-containing fusion protein.

In some embodiments, in the transfecting step the cell is transfected with nucleic acids (iii) encoding an antibody light chain and an antibody heavy chain. In some embodiments, nucleic acid (i) encodes a 3-ketosteroid reductase. In some embodiments, the nucleic acid (ii) encodes the xanthine-guanine phosphoribosyltransferase (Ecogpt) gene.

In some embodiments, a first expression vector comprises nucleic acid (i) and (iii), and a second expression vector comprises nucleic acids (ii). In some embodiments, a first expression vector comprises nucleic acid (i), and a second expression vector comprises nucleic acids (ii) and (iii). In some embodiments, transfection of the first expression vector is performed prior to transfection of the second expression vector. In some embodiments, transfection of the first expression vector is performed simultaneously with transfection of the second expression vector.

In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (i)) in the absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (ii)) in the presence of MPA. In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (i)) in the presence of a 3-ketosteriod reductase inhibitor.

In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol and in the presence of MPA.

In one aspect, the disclosure features methods of manufacturing a therapeutic protein, the method comprising: culturing a cholesterol-auxotrophic and glutamine-auxotrophic cell; transfecting the cell with (i) a nucleic acid encoding a protein which is capable of restoring cholesterol biosynthesis in the cell (e.g., KSR); (ii) a nucleic acid encoding a protein which is capable of restoring glutamine biosynthesis in the cell (e.g., glutathione synthetase); (iii) a nucleic acid encoding a protein which is capable of providing resistance to G418 (e.g., neomycin resistance gene); and (iv) a nucleic acid encoding the therapeutic protein (e.g., an antibody, e.g., a heavy chain and light chain); culturing the cell under conditions suitable for expression of the therapeutic protein; and isolating and/or purifying the therapeutic protein.

In some embodiments, nucleic acid (iii) is transfected first and during and/post transfection G418 is added to the cell culture media. In some embodiments, nucleic acid (iii) is transfected first and during and/or post transfection G418 is added to the cell culture media; and nucleic acid (ii) is transfected second and during and/or post transfection cholesterol is absent from the cell culture media. In some embodiments, nucleic acid (iii) is transfected first and during and/or post transfection G418 is added to the cell culture media; and nucleic acid (ii) is transfected second and during and/or post transfection cholesterol is absent from the cell culture media (e.g., exogenously added cholesterol); and nucleic acid (i) is transfected third and during/post transfection glutamine is absent from the cell culture medium (e.g., exogenously added glutamine) (optionally methionine sulphoximine (MSX) is added to the cell culture media).

In some embodiments, nucleic acid (ii) and (i) are transfected simultaneously, wherein G418 is added to the cell culture media and the cell culture media does not contain cholesterol (e.g., exogenously added cholesterol). In some embodiments, nucleic acids (i), (ii), (iii), and (iv) are transfected simultaneously, wherein the G418 is added to the cell culture media and the cell culture media does not contain cholesterol (e.g., exogenously added cholesterol) and does not contain glutamine (e.g., exogenously added glutamine) (optionally methionine sulphoximine (MSX) is added to the cell culture media). In some embodiments, nucleic acid (iv) is incorporated in the same nucleic acid sequence (e.g., vector) as each of (i), (ii), and (iii). In some embodiments, nucleic acid (iv) is incorporated in the same nucleic acid sequence (e.g., vector) as each of (i) and (ii); (i) and (iii); or (ii) and (iii). In some embodiments, nucleic acid (iv) encodes the heavy and light chain of a therapeutic antibody. In some embodiments, the light chain is incorporated in the same nucleic acid sequence (e.g., vector) as each of (i) and (ii); (i) and (iii); (ii) and (iii); or (i), (ii), and (iii). In some embodiments, the heavy chain is incorporated in the same nucleic acid sequence (e.g., vector) as each of (i) and (ii); (i) and (iii); (ii) and (iii); or (i), (ii), and (iii). In some embodiments, the light chain and heavy chain is incorporated in the same nucleic acid sequence (e.g., vector) as each of (i) and (ii); (i) and (iii); (ii) and (iii); or (i), (ii), and (iii).

In some embodiments, any of nucleic acids (i), (ii), (iii), and (iv) are incorporated into a single nucleic acid (e.g., single vector). For example, in some embodiments, nucleic acids (i) and (ii); (i) and (iii); (i) and (iv); (i), (ii), and (iii); (i), (ii), (iii), and (iv); (ii) and (iii); or (ii) and (iv); (iii) and (iv); are incorporated on a single nucleic acid. In some embodiments, nucleic acid (iv) comprises two separate nucleic acids, one encoding a heavy chain and one encoding a light chain of a therapeutic antibody. In some embodiments the heavy chain is incorporated onto another nucleic acid, e.g., (i), (ii), or (iii). In some embodiments the light chain is incorporated onto another nucleic acid, e.g., (i), (ii), or (iii).

In one embodiment, the cell is an NS0 cell.

In some embodiments, the therapeutic protein is an antibody. In some embodiments, the therapeutic protein is a fusion protein. In some embodiments, the therapeutic protein is an Fc-containing fusion protein.

In some embodiments, in the transfecting step the cell is transfected with nucleic acids (iv) encoding an antibody light chain and an antibody heavy chain. In some embodiments, nucleic acid (i) encodes a 3-ketosteroid reductase. In some embodiments, the nucleic acid (ii) encodes a glutamine synthetase. In some embodiments, the nucleic acid (iii) encodes neomycin resistance gene.

In some embodiments, a first expression vector comprises nucleic acid (i) and (iv), and a second expression vector comprises nucleic acids (ii). In some embodiments, a first expression vector comprises nucleic acid (i), and a second expression vector comprises nucleic acids (ii) and (iv). In some embodiments, transfection of the first expression vector is performed prior to transfection of the second expression vector. In some embodiments, transfection of the first expression vector is performed simultaneously with transfection of the second expression vector.

In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (i)) in the absence of exogenously introduced cholesterol. In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (ii)) in the absence of exogenously introduced glutamine. In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (ii)) in the presence of a glutamine synthetase inhibitor (e.g., methionine sulfoximine). In some embodiments, the cell is cultured (e.g., during and/or after transfection of nucleic acid (i)) in the presence of a 3-ketosteriod reductase inhibitor.

In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol and in the absence of exogenously introduced glutamine. In some embodiments, the cell is cultured in absence of exogenously introduced cholesterol, in the absence of exogenously introduced glutamine, and in the presence of a glutamine synthetase inhibitor (e.g., methionine sulfoximine). In some embodiments, the cell is cultured (e.g., after transfection of nucleic acid (i)) in the absence of exogenously introduced cholesterol and the cell is cultured (e.g., after transfection of nucleic acid (ii)) in the absence of exogenously introduced glutamine.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts an exemplary protocol of the methods described herein.

FIG. 2 depicts the NCBI reference amino acid sequence of 3-ketosteroid reductase (NP_057455) (SEQ ID No. 1).

FIG. 3 depicts the NCBI reference mRNA sequence of HSD17β7 (NM_016371.3) (SEQ ID No. 2).

FIG. 4 depicts the NCBI reference amino acid sequence of glutamine synthetase (NP_002056.2) (SEQ ID No. 3).

FIG. 5A-E depicts the NCBI reference mRNA sequence of glutamine synthetase (NM_002065.6) (SEQ ID No. 4).

FIG. 6 depicts the NCBI reference amino acid sequence of dihydrofolate reductase (DHFR) (NP_000782.1) (SEQ ID No. 5).

FIG. 7A-B depicts the NCBI reference mRNA sequence of DHFR (NM_000791.3) (SEQ ID No. 6).

FIG. 8 depicts the stability of proteins produced using the 3-KSR cell culture system. FIG. 8 lists the final protein titer in the supernatant of 3-KSR cells for 10 different 3-KSR cell clones. Four clones (3-261, 3-330, 3-351, 3-497) demonstrated high protein titer. However, as further shown in FIG. 8 3-KSR clone 3-351, demonstrated a decline in cell specific productivity.

FIG. 9 is a line graph depicting cell selection using Neo (100 μg/ml or 200 μg/ml G418). The graph depicts the cell viability versus days post recovery.

FIG. 10 is a line graph depicting cell selection using glutathione synthetase (GS) (reduce glutamine concentration from 2 mM to 0 mM or from 0.5 mM to 0 mM respectively). The graph depicts the cell viability versus days post recovery.

FIG. 11 is a line graph depicting cell selection using 3-KSR, neo, and GS as a triple selection. The graph depicts the cell viability versus days post recovery. Resistance to G418 can be conferred by neo gene. The concentration of G418 in NS0 is 100 ug/ml and 200 ug/ml; reduce glutamine concentration from 2 mM to 0 mM, or from 0.5 mM to 0 mM. An MSX inhibitor may also be used to inhibit the GS activity.

DETAILED DESCRIPTION OF THE INVENTION

In certain recombinant protein production systems, such as NS0 host cell systems, cholesterol-auxotrophy is exploited by incorporating a 3-ketosteroid reductase (3-KSR) gene into the vector encoding the therapeutic protein, and recombinant cells selected for by removing cholesterol from the culture media (US20100028940). However, the inventors of the present disclosure unexpectedly found that this system can suffer from low productivity (e.g., protein product per cell per day) and low protein titers due to the difficulty of amplification in this cell line (see e.g., FIG. 8). In other NS0 host cell systems, glutamine-auxotrophy is exploited by incorporating a glutamine synthetase (GS) gene into the vector encoding the therapeutic protein, and transfected cells are selected for by removing glutamine from the culture media. In addition, a GS inhibitor can be added to the culture media to drive selection towards the incorporation multiple copies of the GS gene and therefore the gene encoding the protein of interest (Barnes et al. Cytotechnology. 2000. Advances in animal cell recombinant protein production: GS-NS0 expression system February; 32(2):109-23). Each system has different limitations. Described herein are alternate methods of manufacturing therapeutic products in, e.g., an NS0 host cell system.

A “glutamine-auxotrophic” cell as used herein is defined as a cell which does not synthesize any glutamine or does not synthesize enough glutamine to be capable of survival and growth in glutamine-free cell culture medium.

A “cholesterol-auxotrophic” cell as used herein is defined as a cell which does not synthesize any cholesterol or does not synthesize enough cholesterol to be capable of survival and growth in cholesterol-free cell culture medium.

“Restoring glutamine biosynthesis” as used herein means increasing the level of glutamine biosynthesis in a cell (from the level in a glutamine-auxotrophic cell), to at least a level which enables the cell to survive and grow in glutamine-free cell culture medium.

“Restoring cholesterol biosynthesis” as used herein means increasing the level of cholesterol biosynthesis in a cell (from the level in a cholesterol-auxotrophic cell), to at least a level which enables the cell to survive and grow in cholesterol-free cell culture medium.

“Survive and grow” or “survival and growth” as used herein refers to the ability of a cell or culture of cells to maintain greater than 60% cell viability during log phase growth as measured by trypan blue exclusion.

3-Ketosteroid Reductase (KSR)

The enzyme 3-ketosteroid reductase is encoded by the HSD17β7 gene, and functions as a 3-ketosteroid reductase in the biosynthesis of cholesterol (Marijanovic et al., Mol Endocrinol. 2003 September; 17(9):1715-25). See FIG. 2 (SEQ ID No. 1) and FIG. 3 (SEQ ID No. 2) respectively, for NCBI reference amino acid (NP_057455) and mRNA sequence (NM_016371.3).

Glutamine Synthetase (GS)

The enzyme glutamine synthetase encoded by the glutamine synthetase gene catalyzes the synthesis of glutamine from glutamate and ammonia (Eisenberg et al., Biochimica et Biophysica Acta, 2000, Vol 1477, 122-145). Several alternatively spliced transcript variants have been found for this gene. See FIG. 4 (SEQ ID No. 3) and FIG. 5 (SEQ ID No. 4) respectively, for NCBI reference amino acid NP_002056.2 and mRNA sequence NM_002065.6.

Dihydrofolate Reductase (DHFR)

The enzyme DHFR is encoded by the DHFR gene, and converts dihydrofolate into tetrahydrofolate, a methyl group shuttle required for the de novo synthesis of purines, thymidylic acid, and certain amino acids. Several alternatively spliced transcript variants have been found for this gene. See FIG. 6 (SEQ ID No. 5) and FIG. 7 (SEQ ID No. 6) respectively, for NCBI reference amino acid (NP_000782.1) and mRNA sequence (NM_000791.3).

Antibiotic Resistance Gene Selection Markers

Antibiotic resistance genes are commonly used positive selection markers used in mammalian cell culture (see e.g., Antibody Expression and Production, Editor Mohamed Al-Rubeai, Springer Netherlands, Springer Science Business Media B.V., ISBN 978-94-007-1256-0; Cell Line Development, Mohamed Al-Rubeai Aug. 11, 2009 Springer Science & Business Media). Exemplary antibiotic resistance genes include but are not limited to genes conferring resistance to neomycin resistance gene, blasticidin, hygromyocin, puromycin, zeocin, mycophenolic acid. Suitable antibiotic resistance genes and corresponding inhibitors for use in cell selection would be known to one of skill in the art.

TABLE 1 Exemplary Antibiotic Selection Markers Antibiotic Mechanism of Action Resistance Gene Hygromycin Hygromycin B is an The hph gene. B aminoglycoside antibiotic produced by Streptomyces hygroscopicus. Hygromycin B inhibits protein synthesis. It has been reported to interfere with translocation and to cause mistranslation at the 70S ribosome. Zeocin ® Zeocin ® is a copper-chelated The Sh ble gene. glycopeptide antibiotic produced by Streptomyces CL990. Zeocin ™ causes cell death by intercalating into DNA and cleaving it. Blasticidin Blasticidin is a peptidyl nucleoside The blasticidin antibiotic isolated from resistance gene Streptomyces griseochromogenes from Bacillus that inhibits protein synthesis by cereus (bsr), which interfering with the peptide-bond codes for blasticidin- formation in the ribosomal S deaminase. machinery. Puromycin Puromycin is an aminonucleoside The Pac gene encoding antibiotic produced by a puromycin N-acetyl- Streptomyces alboniger. It transferase (PAC) that specifically inhibits peptidyl was found in a transfer on both prokaryotic and Streptomyces producer eukaryotic ribosomes. strain. Geneticin G418 (Geneticin) is an The Neomycin aminoglycoside antibiotic similar resistance gene in structure to gentamicin B1, (neo) from Tn5 produced by Micromonospora encoding an rhodorangea. G418 blocks aminoglycoside 3′- polypeptide synthesis by inhibiting phosphotransferase, the elongation step in both APH 3′ II. prokaryotic and eukaryotic cells. Phleomycin Phleomycin is a glycopeptide The Sh ble gene from antibiotic of the bleomycin family, Streptoalloteichus isolated from a mutant strain of hindustanus which Streptomyces verticillus. It binds encodes a protein that and intercalates DNA thus binds to phleomycin, destroying the integrity of the inhibiting its DNA double helix. cleavage activity.

Vectors, Host Cells, and Therapeutic Protein Production

The therapeutic proteins of the invention can be produced from a host cell. A host cell refers to a vehicle that includes the necessary cellular components, e.g., organelles, needed to express the polypeptides and constructs described herein from their corresponding nucleic acids. The nucleic acids may be included in nucleic acid vectors that can be introduced into the host cell by conventional techniques known in the art (e.g., transformation, transfection, electroporation, calcium phosphate precipitation, direct microinjection, infection, etc). The choice of nucleic acid vectors depends in part on the host cells to be used. Generally, preferred host cells are of either prokaryotic (e.g., bacterial) or eukaryotic (e.g., mammalian) origin.

Nucleic Acid Vector Construction and Host Cells

A nucleic acid sequence encoding the amino acid sequence of a therapeutic protein of the invention may be prepared by a variety of methods known in the art. These methods include, but are not limited to, oligonucleotide-mediated (or site-directed) mutagenesis and PCR mutagenesis. A nucleic acid molecule encoding a therapeutic protein of the invention may be obtained using standard techniques, e.g., gene synthesis. Alternatively, a nucleic acid molecule encoding a wild-type therapeutic protein may be mutated to contain specific amino acid substitutions using standard techniques in the art, e.g., QuikChange™ mutagenesis. Nucleic acid molecules can be synthesized using a nucleotide synthesizer or PCR techniques.

Nucleic acid sequences encoding a therapeutic protein of the invention may be inserted into a vector capable of replicating and expressing the nucleic acid molecules in prokaryotic or eukaryotic host cells. Many vectors are available in the art and can be used for the purpose of the invention. Each vector may contain various components that may be adjusted and optimized for compatibility with the particular host cell. For example, the vector components may include, but are not limited to, an origin of replication, a selection marker gene, a promoter, a ribosome binding site, a signal sequence, the nucleic acid sequence encoding protein of interest, and a transcription termination sequence.

In one example, vectors of the invention include: a vector comprising a weak promoter for a selection gene (e.g., 3-ketosteroid reductase and glutamine synthetase) and a strong promoter for the gene encoding the protein of interest (e.g., an antibody, e.g., heavy and light chain of an antibody). Vectors can be linearized or supercoiled exhibiting improved transfection efficiency. In some embodiments, codon optimization of the vector is employed to minimize the use of rare codons in the coding sequence and improve protein production yields. Exemplary vectors of the invention are described in Wurm (2004) Nature Biotechnology, Vol 22; Issue 11: 1393-1398).

In some embodiments, mammalian cells are used as host cells for the invention. The glutamine-auxotrophic and cholesterol-auxotrophic phenotype can be induced by genetic manipulation of a non-glutamine-auxotrophic and non-cholesterol-auxotrophic cell, including for example mutation or deletion of a gene necessary for endogenous glutamine biosynthesis, such as glutamine synthetase. Common methods of genetic engineering are well known to those of skill in the art, e.g., site directed mutagenesis, zinc finger nucleases, shRNA, transposons, See e.g., Cytotechnology. 2007 April; 53(1-3): 65-73. The murine myeloma cells termed NS0 are known glutamine-auxotrophic and cholesterol-auxotrophic cells (See e.g., Barnes et al. Cytotechnology. 2000. Advances in animal cell recombinant protein production: GS-NS0 expression system February; 32(2):109-23; and US 20100028940).

Additional examples of mammalian cell types which may be manipulated to be used as host cells include, but are not limited to, human embryonic kidney (HEK) (e.g., HEK293, HEK 293F), Chinese hamster ovary (CHO), HeLa, COS, PC3, Vero, MC3T3, NS0, VERY, BHK, MDCK, W138, BT483, Hs578T, HTB2, BT20, T47D), CRL7030, and HsS78Bst cells. In other embodiments, E. coli cells are used as host cells for the invention. Examples of E. coli strains include, but are not limited to, E. coli 294 (ATCC® 31,446), E. coli λ, 1776 (ATCC® 31,537, E. coli BL21 (DE3) (ATCC® BAA-1025), and E. coli RV308 (ATCC® 31,608). Different host cells have characteristic and specific mechanisms for the posttranslational processing and modification of protein products. Appropriate cell lines or host systems may be chosen to ensure the correct modification and processing of the therapeutic protein expressed. The above-described expression vectors may be introduced into appropriate host cells using conventional techniques in the art, e.g., transformation, transfection, electroporation, calcium phosphate precipitation, and direct microinjection. Once the vectors are introduced into host cells for protein production, host cells are cultured in conventional nutrient media modified as appropriate for inducing promoters, selecting transformants, or amplifying the genes encoding the desired sequences. Methods for expression of therapeutic proteins are known in the art, see, for example, Paulina Balbas, Argelia Lorence (eds.) Recombinant Gene Expression: Reviews and Protocols (Methods in Molecular Biology), Humana Press; 2nd ed. 2004 (Jul. 20, 2004) and Vladimir Voynov and Justin A. Caravella (eds.) Therapeutic Proteins: Methods and Protocols (Methods in Molecular Biology) Humana Press; 2nd ed. 2012 (Jun. 28, 2012).

Protein Production, Recovery, and Purification

Host cells used to produce a therapeutic protein of the invention may be grown in media known in the art and suitable for culturing of the selected host cells. Examples of suitable media for mammalian host cells include Minimal Essential Medium (MEM), Dulbecco's Modified Eagle's Medium (DMEM), Expi293™ Expression Medium, DMEM with supplemented fetal bovine serum (FBS), and RPMI-1640. Examples of suitable media for bacterial host cells include Luria broth (LB) plus necessary supplements, such as a selection agent, e.g., ampicillin. Host cells are cultured at suitable temperatures, such as from about 20° C. to about 39° C., e.g., from 25° C. to about 37° C., preferably 37° C., and CO₂ levels, such as 5 to 10% (preferably 8%). The pH of the medium is generally from about 6.8 to 7.4, e.g., 7.0, depending mainly on the host organism. If an inducible promoter is used in the expression vector of the invention, protein expression is induced under conditions suitable for the activation of the promoter. Conventional cell culture conditions for production of a therapeutic protein are known in the art, e.g., see Butler, Cell Culture and Upstream Processing, Taylor & Francis; 1st edition (May 25, 2007).

Protein recovery typically involves disrupting the host cell, generally by such means as osmotic shock, sonication, or lysis. Once the cells are disrupted, cell debris may be removed by centrifugation or filtration. The proteins may be further purified. An antibody of the invention may be purified by any method known in the art of protein purification, for example, by protein A affinity, other chromatography (e.g., ion exchange, affinity, and size-exclusion column chromatography), centrifugation, differential solubility, or by any other standard technique for the purification of proteins. (see Process Scale Purification of Antibodies, Uwe Gottschalk (ed.) John Wiley & Sons, Inc., 2009). In some instances, a therapeutic protein can be conjugated to marker sequences, such as a peptide to facilitate purification. An example of a marker amino acid sequence is a hexa-histidine peptide (His-tag), which binds to nickel-functionalized agarose affinity column with micromolar affinity. Other peptide tags useful for purification include, but are not limited to, the hemagglutinin “HA” tag, which corresponds to an epitope derived from the influenza hemagglutinin protein.

Pharmaceutical Compositions and Preparations

The invention features pharmaceutical compositions that include one or more therapeutic protein described herein. In addition to a therapeutically effective amount of the therapeutic protein, the pharmaceutical compositions may contain one or more pharmaceutically acceptable carriers or excipients, which can be formulated by methods known to those skilled in the art.

Acceptable carriers and excipients in the pharmaceutical compositions are nontoxic to recipients at the dosages and concentrations employed. Acceptable carriers and excipients may include buffers, antioxidants, preservatives, polymers, amino acids, and carbohydrates. Pharmaceutical compositions of the invention can be administered parenterally in the form of an injectable formulation. Pharmaceutical compositions for injection (i.e., intravenous injection) can be formulated using a sterile solution or any pharmaceutically acceptable liquid as a vehicle. Pharmaceutically acceptable vehicles include, but are not limited to, sterile water, physiological saline, and cell culture media (e.g., Dulbecco's Modified Eagle Medium (DMEM), α-Modified Eagles Medium (α-MEM), F-12 medium). Formulation methods are known in the art, see e.g., Banga (ed.) Therapeutic Peptides and Proteins: Formulation, Processing and Delivery Systems (2nd ed.) Taylor & Francis Group, CRC Press (2006).

The pharmaceutical composition may be formed in a unit dose form as needed. The amount of active component, e.g., one or more therapeutic protein of the invention included in the pharmaceutical preparations is such that a suitable dose within the designated range is provided (e.g., a dose within the range of 0.01-500 mg/kg of body weight).

Therapeutic Proteins

Therapeutic proteins which may be made by the methods described herein include any recombinant therapeutic protein of interest or biosimilar thereof, including but limited to, antibodies (e.g., monoclonal antibodies, bispecific antibodies, multispecific antibodies), fusion proteins (e.g., Fc fusion), anticoagulants, blood factors, bone morphogenetic proteins, engineered protein scaffolds, enzymes, growth factors, hormones, hormone releasing factors, interferons, interleukins, and thrombolytics. Therapeutic proteins include both glycosylated (e.g., proteins having at least one oligosaccharide chain) and non-glycosylated proteins.

Exemplary monoclonal antibodies include, but are not limited to adalimumab, infiliximab, palivizumab, cetuximab, natalizumab, eculizumab, ustekinumab, golimumab, ofatumab, canakinumab, belimumab, alirocumab, mepolizumab, necitumumab, nivolumab, dinutuximab, secukinumab, evolocumab, blinatumomab, pembrolizumab, ramucirumab, vedolizumab, siltuximab, obinutuzumab, trastuzumab, raxibacumab, pertuzumab, brentuximab, ipilimumab, denosumab, tocilizumab, ofatumumab, canakinumab, certolizumab, catumaxomab, ranibizumab, panitumumab, bevacizumab, cetuximab, efalizumab, omalizumab, tositumomab, ibritumomab, alemtuzumab, gemtuzumab, basiliximab, daclizumab, rituximab, and abciximab.

Exemplary fusion proteins include, but are not limited to alefacept, entanercept, abatacept, belatacept, aflibercept, ziv-aflibercept, rilonacept, romiplostim, apocept, trebananib, blisibimod, and dulaglutide.

OTHER EMBODIMENTS

This invention is further illustrated by the following examples that should not be construed as limiting. The contents of all references, patents and published patent applications cited throughout this application are incorporated herein by reference.

EXAMPLES Example 1. Manufacture of Therapeutic Antibodies Utilizing a Double Auxotrophic Cell

The following Example describes methods of manufacturing therapeutic proteins, such as antibodies, comprising expression of the therapeutic protein of interest in a cholesterol-auxotrophic and glutamine-auxotrophic cell. The method desirably allows for increased amplification and copy number of the gene of interest, and production in the absence of cholesterol, which is highly insoluble in aqueous solutions and very challenging to work with. The exemplary method is further outlined in FIG. 1.

Glutamine-auxotrophic and cholesterol-auxotrophic cells, such as NS0 cells, are transfected with a first vector comprising a nucleic acid encoding a 3-ketosteroid reductase (3-KSR). During and post this first transfection, the cells are maintained in cholesterol-free culture media to select for cells which express the first vector, thereby producing a 3-KSR expressing glutamine-auxotrophic culture of cells. These cells are simultaneously or subsequently transfected with a second vector comprising a nucleic acid encoding a glutamine synthetase (GS) and the protein of interest, e.g., the heavy and light chain of a therapeutic antibody. During and post this second transfection, the cells are maintained in glutamine-free cell culture media to select for cells which express the second vector. To further select for cells which have incorporated multiple copies of the second vector, the cell culture media during and/or after the second transfection is supplemented with a glutamine synthetase inhibitor such as methionine sulfoximine (MSX). The final 3-KSR-GS antibody producing cells can be maintained in a cholesterol-free medium, avoiding cholesterol associated manufacturing problems, and display a high level of productivity derived from the MSX selection.

Example 2: Cell Viability Assay

The following example describes a trypan blue assay to determine cell viability as a proxy for cells that exhibit adequate survival and growth.

Prepare a 0.4% solution of trypan blue in buffered isotonic salt solution, pH 7.2 to 7.3 (i.e., phosphate-buffered saline). Add 0.1 mL of trypan blue stock solution to 1 mL of cells. Load a hemocytometer and examine immediately under a microscope at low magnification. Count the number of blue staining cells and the number of total cells. Cell viability is calculated as the number of viable cells divided by the total number of cells within the grids on the hemocytometer. If cells take up trypan blue, they are considered non-viable. Cell viability is at least 90% for healthy log-phase cultures.

% viable cells=[1.00−(Number of blue cells÷Number of total cells)]×100

The cell density of the cell line suspension can be determined using a hemocytometer. To calculate the number of viable cells per mL of culture, the following formula is used, correcting for the dilution factor: Number of viable cells×10E4×1.1=cells/mL culture.

Example 3. Manufacture of Therapeutic Antibodies Utilizing a Triple Selection Method

The following Example describes methods of manufacturing therapeutic proteins, such as antibodies, comprising expression of the therapeutic protein of interest in a cholesterol- and glutamine-auxotrophic cell with an additional third selection mechanism, e.g., neomycin resistance gene (e.g., using G418 for selection). The method desirably allows for increased amplification and copy number of the gene of interest, and production in the absence of cholesterol, which is highly insoluble in aqueous solutions and very challenging to work with, while overcoming the unexpected manufacturing challenges associated with the 3-KSR cell culture selection system, including for example low productivity.

NS0 cell selection was first optimized using both a single neomycin selection (FIG. 9) and a single GS selection (FIG. 10). For neomycin optimization, cells were transfected according to standard practice with a nucleic acid vector encoding a neomycin resistance gene. Neomycin was then added to the cell culture media at either (100 μg/ml or 200 μg/ml) for selection. Cell viability was measured at the denoted days post recovery. For GS based selection, cells were transfected with a nucleic acid vector encoding GS and maintained in glutamine-fee cell culture media. Cell viability was measured at the denoted days post recovery. A 3-KSR based triple selection method was optimized using neomycin, 3-KSR, and GS selection to overcome the unexpectedly low productivity associated with 3-KSR selection (FIG. 8). Cells were transfected according to standard practice with one or more nucleic acid vector encoding 3-KSR, GS, and neomycin resistance gene. For selection, cells were maintained in the absence of glutamine and cholesterol and in the presence of neomycin. As shown in FIG. 11, the triple selection maintained ample cell viability post recovery. 

1.-42. (canceled)
 43. A method of manufacturing a therapeutic protein, comprising: transfecting a cholesterol-auxotrophic cell with (i) a nucleic acid encoding a protein that restores cholesterol biosynthesis in the cell; (ii) an aminoglycosidic antibiotic resistance gene; and (iii) a nucleic acid encoding the therapeutic protein.
 44. The method of claim 43, wherein the protein that restores cholesterol biosynthesis in the cell is a 3-ketosteroid reductase (3-KSR).
 45. The method of claim 43, wherein the aminoglycosidic antibiotic resistance gene is selected from the group consisting of: a neomycin resistance gene, a blasticidin resistance gene, a hygromycin resistance gene, a puromycin resistance gene, a zeocin resistance gene, and a mycophenolic acid resistance gene.
 46. The method of claim 43, comprising transfecting the cell with a first vector and a second vector, wherein the first vector comprises the nucleic acid encoding the protein that restores cholesterol biosynthesis in the cell and the nucleic acid encoding the therapeutic protein; and the second vector comprises the aminoglycosidic antibiotic resistance gene.
 47. The method of claim 43, comprising transfecting the cell with a first vector and a second vector, wherein the first vector comprises the nucleic acid encoding the protein that restores cholesterol biosynthesis in the cell; and the second vector comprises the antibiotic resistance gene and the nucleic acid encoding the therapeutic protein.
 48. The method of claim 43, comprising transfecting the cell with a first vector and a second vector, wherein the first vector comprises the nucleic acid encoding the protein that restores cholesterol biosynthesis in the cell and the nucleic acid encoding the therapeutic protein; and the second vector comprises the antibiotic resistance gene and the nucleic acid encoding the therapeutic protein
 49. The method of claim 46, wherein the method comprises transfecting the cell with the first vector and the second vector, and wherein the transfecting the cell with the first vector is carried out prior to the transfecting with the second vector, or the transfecting the cell with the first vector is carried out after the transfecting with the second vector.
 50. The method of claim 47, wherein the method comprises transfecting the cell with the first vector and the second vector, and wherein the transfecting the cell with the first vector is carried out prior to the transfecting with the second vector, or the transfecting the cell with the first vector is carried out after the transfecting with the second vector.
 51. The method of claim 48, wherein the method comprises transfecting the cell with the first vector and the second vector, and wherein the transfecting the cell with the first vector is carried out prior to the transfecting with the second vector, or the transfecting the cell with the first vector is carried out after the transfecting with the second vector.
 52. The method of claim 46, wherein the method comprises transfecting the cell with the first vector and the second vector, and wherein the transfecting the cell with the first vector is carried out simultaneously with the transfecting the cell with the second vector.
 53. The method of claim 47, wherein the method comprises transfecting the cell with the first vector and the second vector, and wherein the transfecting the cell with the first vector is carried out simultaneously with the transfecting the cell with the second vector.
 54. The method of claim 48, wherein the method comprises transfecting the cell with the first vector and the second vector, and wherein the transfecting the cell with the first vector is carried out simultaneously with the transfecting the cell with the second vector.
 55. The method of claim 43, further comprising culturing the cell in the presence of a 3-KSR inhibitor after transfecting the cell with (i).
 56. The method of claim 43, further comprising culturing the cell in the absence of at exogenously introduced cholesterol after transfecting with (i).
 57. The method of claim 43, further comprising culturing the cell n the presence of an aminoglycosidic antibiotic after transfecting the cell with (ii).
 58. The method of claim 52, comprising culturing the cell in the absence of an exogenously introduced cholesterol and in the presence of an aminoglycosidic antibiotic after simultaneously transfecting the cell with the first vector and the second vector.
 59. The method of claim 53, comprising culturing the cell in the absence of an exogenously introduced cholesterol and in the presence of an aminoglycosidic antibiotic after simultaneously transfecting the cell with the first vector and the second vector.
 60. The method of claim 54, comprising culturing the cell in the absence of an exogenously introduced cholesterol and in the presence of an aminoglycosidic antibiotic after simultaneously transfecting the cell with the first vector and the second vector.
 61. The method of claim 43, wherein the nucleic acid encoding the therapeutic protein comprises a nucleic acid encoding a heavy chain and a light chain of an antibody.
 62. The method of claim 61, wherein the antibody is selected from the group consisting of: adalimumab, infiliximab, palivizumab, cetuximab, natalizumab, eculizumab, ustekinumab, golimumab, ofatumab, canakinumab, belimumab, alirocumab, mepolizumab, necitumumab, nivolumab, dinutuximab, secukinumab, evolocumab, blinatumomab, pembrolizumab, ramucirumab, vedolizumab, siltuximab, obinutuzumab, trastuzumab, raxibacumab, pertuzumab, brentuximab, ipilimumab, denosumab, tocilizumab, ofatumumab, canakinumab, certolizumab, catumaxomab, ranibizumab, panitumumab, bevacizumab, cetuximab, efalizumab, omalizumab, tositumomab, ibritumomab, alemtuzumab, gemtuzumab, basiliximab, daclizumab, rituximab, abciximab, alefacept, entanercept, abatacept, belatacept, aflibercept, ziv-aflibercept, rilonacept, romiplostim, apocept, trebananib, blisibimod, and dulaglutide.
 63. The method of claim 43, wherein the therapeutic protein is selected from the group consisting of: an antibody, a fusion protein, an anticoagulant, a blood factor, a bone morphogenic protein, an engineered protein scaffold, an enzyme, a growth factor, a hormone, a hormone releasing factor, an interleukin, or a thrombolytic protein and the method comprises transfecting the cell with a nucleic acid encoding an antibody, a fusion protein, an anticoagulant, a blood factor, a bone morphogenic protein, an engineered protein scaffold, an enzyme, a growth factor, a hormone, a hormone releasing factor, an interferon, an interleukin, and a thrombolytic protein.
 64. The method of claim 43, wherein the cell is an NS0 cell.
 65. A transformed mammalian host cell, transfected with an aminoglycosidic antibiotic resistance gene, and a nucleic acid encoding a therapeutic protein, wherein the transformed mammalian host cell is derived from a parental mammalian host cell that is cholesterol-auxotrophic.
 66. A therapeutic protein produced by a method comprising culturing the transformed mammalian host cell of claim 65, in the presence of an aminoglycosidic antibiotic. 